Fuel injection control method for a direct-injection internal-combustion engine

Abstract

The present invention relates to a fuel injection control method for a direct-injection internal-combustion engine comprising at least an injector ( 20 ) of fuel jet nappe angle (a 1 ), a cylinder ( 10 ), a cylinder head ( 12 ), a piston ( 18 ) sliding in this cylinder and connected to a crankshaft, and a combustion chamber delimited by wall ( 26 ) of the cylinder, cylinder head ( 12 ) and upper face ( 24 ) of piston ( 18 ). According to the invention, the method consists in determining a lower limit position (PL) of piston ( 18 ) below which wall ( 26 ) of the cylinder is likely to be wetted by the fuel jets coming from the injector, in determining the effective position of this piston, in locating this effective position of the piston in relation to the lower limit position and in adjusting the fuel injection parameters according to the effective position of the piston in relation to the lower limit position.

What is claimed is:  
     
       1. A fuel injection control method intended for a direct-injection internal-combustion engine comprising at least an injector ( 20 ) of fuel jet nappe angle (a 1 ), a cylinder ( 10 ), a cylinder head ( 12 ), a piston ( 18 ) sliding in this cylinder and connected to a crankshaft, and a combustion chamber delimited by wall ( 26 ) of the cylinder, cylinder head ( 12 ) and upper face ( 24 ) of piston ( 18 ), characterised in that it consists in: 
       determining a lower limit position (PL) of piston ( 18 ) below which wall ( 26 ) of the cylinder is likely to be wetted by the fuel jets from the injector,  
       determining the effective position of this piston,  
       locating this effective position of the piston in relation to the lower limit position,  
       adjusting the fuel injection parameters according to the effective position of the piston in relation to the lower limit position.  
     
     
       2. A method as claimed in  claim 1 , characterised in that it consists in adjusting injection parameters so as to limit the penetration of fuel jets in the combustion chamber for any position of piston ( 18 ) between its lower limit position (PL) and its furthest position from cylinder head ( 12 ). 
     
     
       3. A method as claimed in  claim 2 , characterised in that it consists in injecting a determined amount of fuel under very high pressure. 
     
     
       4. A method as claimed in  claim 3 , characterised in that it consists in injecting a determined amount of fuel under a pressure above 1000 bars. 
     
     
       5. A method as claimed in  claim 2 , characterised in that it consists in injecting a determined amount of fuel for a very short length of time. 
     
     
       6. A method as claimed in  claim 3 , characterised in that it consists in repeating the injection of a determined amount of fuel until the total amount of fuel to be injected is obtained. 
     
     
       7. A method as claimed in  claim 3 , characterised in that it consists in injecting a determined amount that does not exceed 25% of the total amount of fuel to be injected. 
     
     
       8. A method as claimed in  claim 1 , characterised in that it consists in determining the lower limit position (PL) of the piston by means of the relation D×tan(a 1 /2), where D is the radial distance between the point of origin O of the fuel jets and wall ( 26 ) of cylinder ( 10 ). 
     
     
       9. A method as claimed in  claim 1 , characterised in that it consists in using injection parameters to inject the fuel in a conventional way for any position of piston ( 18 ) between its lower limit position (PL) and its closest position to cylinder head ( 12 ).